Prescribed fires were applied to ponderosa pine-incense-cedar and white fir-giant sequoia ecosystems in the southern Sierra Nevada. Aerial and heavy fuels were not affected, but weight, depth, and water-holding capacity of fine fuels were reduced. Forest floor wettability was altered, and some water repellency was transferred to the soil. Soil physical properties were slightly affected: one index of soil water repellency, the capillary rise index, increased. Another index, the water drop penetration time, was not increased. Bulk density was not affected, and even though per cent carbon slightly decreased, the grams per square meter of carbon was not affected. Water runoff, and to a lesser degree sediment yield, were increased by burning. The increases were most highly correlated to the decrease in the forest floor. A computer model using depth of forest floor as an index of runoff and erosion hazard was developed and showed that prescribed fires could be used in ecosystem management without generating erosion hazards of significance.